Effect Of Process Parameters And Friction Material On Metal Flow And Microstructure Of Al/Mg FSW Weld

The composite structure of Al/Mg dissimilar alloy has the advantage of light weight,but it is difficult to get high quality welded joint by traditional fusion welding.The difficulty of thick plate Al/Mg dissimilar alloy friction stir welding is that the joint is easy to form intermetallic compounds and the microstructure is different along the thickness direction,it is great significance to study the flow law of the plastic metal in the weld and the change law of the joint structure.In this paper,the bottom heating and the friction material on the weld surface are used to weld the thick plate Al/Mg dissimilar alloy,the effects of process parameters and friction material properties on weld formation,plastic metal flow and joint structure were investigated.By observing the shape of the bottom of the weld nugget zone and measuring the parameters of the bottom of the weld nugget zone,the flow law of the plastic metal in the weld zone is revealed,and the microstructure and composition of the weld are analyzed,and the change law of the joint structure is grasped.The results show that compared with 5A03 aluminum alloy,1060 aluminum as friction material has better weld shape.When the rotating speed is 750 rpm and the welding speed is 23.5 mm/min?37.5 mm/min,the well-formed weld can be obtained with 1060 pure aluminum as friction material.The onion petal pattern formed at the bottom of the nugget zone is composed of alternate annular Al/Mg mechanical mixture and aluminum alloy structure.The rotation speed of the stirring head was increased,the plastic metal was mixed evenly,and the pattern of onion petals disappeared gradually.In a certain range,the n/v value can be used to characterize the heat input of the weld.The larger the n/v value is,the more the axial migration of the plastic metal in the unit length weld is,which shows that the area at the bottom of the weld area is increasing.The types of intermetallic compounds produced at the interface and the nugget zone are dominated by the composition of the interface,the content of magnesium in the liquefaction zone of the magnesium side interface is higher and the eutectictructure of Al₁₂Mg₁₇+?-Mg is formed,and the content of magnesium in the liquefaction zone of the aluminum side interface and the nugget zone is lower,Al₃Mg₂+?-Al eutectic structure was formed.The liquefaction zone of the magnesium side interface is formed between the aluminum alloy structure and the magnesium alloy parent material,and the range of the eutectic structure is dominated by temperature.When the welding speed is 23.5mm/min and the rotating speed is 750 rpm,the width of eutectic layer is 240?m and49?m respectively.The aluminum content in the aluminum side interface and the upper part of the nugget zone is higher than that in the middle part and the lower part,which results in the less intermetallic compound content in the aluminum side interface and the upper part of the nugget zone,the lower part of the interface has less intermetallic compounds than the middle part and higher than the upper part,and the lower part of the nugget zone has low temperature and no eutectic reaction.The S-curve on the magnesium side can be eliminated by increasing the rotating speed of the stirring head.At low rotating speed and high welding speed,the eutectic structure range formed at the interface between the magnesium side and the aluminum side is obviously reduced.